P0131moderate severityPowertrain
O2 Sensor Circuit Low Voltage Bank 1 Sensor 1
on 2005 Audi A4 3.0L V6 · AWD
What this code means
The upstream O2 sensor voltage on Bank 1 is staying below 0.45V, indicating a lean condition or sensor fault.
Symptoms
- Check Engine Light
- Lean running
- Poor fuel economy
- Rough idle
Common causes
- Vacuum leak
- Faulty O2 sensor
- Exhaust leak before sensor
- Low fuel pressure
- Faulty fuel injector
Diagnostic steps
- Check for vacuum leaks
- Monitor O2 sensor voltage
- Test fuel pressure
- Perform smoke test on intake
- Inspect O2 sensor
Repair notes
Fix vacuum or exhaust leak. Replace O2 sensor if confirmed faulty.
Other Powertrain codes on this vehicle
P0001
Fuel Volume Regulator Control Circuit/Open
P0002
Fuel Volume Regulator Control Circuit Range/Performance
P0003
Fuel Volume Regulator Control Circuit Low
P0004
Fuel Volume Regulator Control Circuit High
P0010
Intake Camshaft Position Actuator Circuit/Open Bank 1
P0011
Intake Camshaft Position Timing Over-Advanced Bank 1
P0012
Intake Camshaft Position Timing Over-Retarded Bank 1
P0013
Exhaust Camshaft Position Actuator Circuit/Open Bank 1
P0014
Exhaust Camshaft Position Timing Over-Advanced Bank 1
P0015
Exhaust Camshaft Position Timing Over-Retarded Bank 1